# std::flat_map<Key,T,Compare,KeyContainer,MappedContainer>::extract

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< cpp‎ | container‎ | flat map

containers extract() &&; |  | (since C++23)

Extracts adapted containers `c`. Equivalent to return std::move(c);.

After this operation *this is empty, even if an exception is thrown.

### Parameters

(none)

### Return value

std::move(c).

### Complexity

Constant.

### Example

Run this code

    #include <cassert>
    #include <flat_map>
    #include <print>
    #include <type_traits>
    #include <vector>

    int main()
    {
        std::flat_map<int, double> map{{1, 1.1}, {2, 2.2}, {3, 3.3}};
        const auto size = map.size();

        auto c = map.extract();
        assert(c.keys.size() == size);
        assert(c.values.size() == size);
        assert(map.empty());
        assert(map.keys().empty());
        assert(map.values().empty());

        // The default keys and values containers are std::vector:
        static_assert(std::is_same_v<decltype(c.keys), std::vector<int>>);
        static_assert(std::is_same_v<decltype(c.value), std::vector<int>>);

        std::println("keys: {}", c.keys);
        std::println("values: {}", c.values);
    }

Output:

    keys: [1, 2, 3]
    values: [1.1, 2.2, 3.3]

### See also

replace | replaces the underlying containers (public member function)

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